It’s a good question but I don’t place any confidence in gut feelings, so my answer would be the likely range of the AR5. I found Kahneman’s discussion convincing in “Thinking, fast and slow” of the ways in which intuition misleads us, and in particular that experts are overconfident.

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24 thoughts on “Climate sensitivity, again”

“The thing is, my gut feeling is that the starlight I see when I look up at night can’t possibly have been emitted long before I was born, and that quantum mechanical entanglement of two particles at a distance can’t happen, but I know these feelings are wrong. So I trust the research and not my feeling on climate too and hence go with the studies’ results that from multiple lines of evidence point to 2-4.5C for the most credible papers.”

And the runner up is Ken Caldeira:

“Earth System sensitivity is a bit more complicated as it might make more sense to think about sensitivity to an emissions rather than a concentration. The idea of doubling or quadrupling CO2 and then holding it constant for many thousands of years is a bit artificial, especially if you are considering biogeochemical feedbacks to be included in your definition of climate sensitivity.”

I was always amused one revealing response from Granger Morgan’s expert elicitation on climate sensitivity a long time ago. While the various experts were labeled anonymously, it is very clear which climate sensitivity distribution comes from Lindzen. Not only is his central estimate wacky (a 0.3 degree CS?!) but even worse were the ridiculously small uncertainty bounds that were around that central estimate. When one’s uncertainty bounds don’t even come close to including the central estimate of the rest of the scientific field, that indicates something about one’s arrogance and/or intellectual dishonesty.

Yes, see this tweet fro ma few days ago, with Morgan+Keith’s original forest plot, and my replot, which makes even clearer what an outiier Expert #5 (had to be RSL) was.
Steve Schneider of course worked very hard to get people to understand and express uncertainty, and he once told me Lindzen’s certainty was the most frustrating thing about him.

“Yes, the science is settled – and yes, of course there are also uncertainties. Climate sensitivity is perhaps the most important one…”

If the climate SCIENCE is SETTLED, why would there also be uncertainties?

And if the climate science is settled, then I’d suppose these 13 climate scientists (and all the others who write about CAGW) can move on to other topics or careers.
They can leave the rest of the work to economists and politicians to work out cost/benefit analyses for possible anthropogenic solutions.
And to voters to weigh in on whether they “buy” those cost/benefit analyses.
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Assuming the 13 experts are basing their gut feel (of how global temperatures will change with a doubling of CO2) on climate models, how accurate have those same climate models been in predicting current global temperatures based on CO2 levels of the last 200 years or so?
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I found this while Googling tonight. I don’t know what these 13 experts would say about it, but it’s kind of pretty. A pretty rollercoaster.http://www.longrangeweather.com/global_temperatures.htm

Gravity has some significant uncertainties. Quantum gravity, around black holes, force unification, and more. Not very long ago, I could list gravity waves in this. We have just made a little progress…

Don’t let this uncertainty convince you that jumping off of a 828 meter high building like the Burj Khalifa without a parachute is a good idea. The science is settled.

If we burn all of the potentially available fossil fuels, we will increase the CO2 level in the atmosphere by about 4 times. (There is some uncertainty here as well. How much fossil fuel extraction is technically or economically possible?) If the climate sensitivity is low, we will only increase the surface temperature by about 8C.

Add 8C to the temperature and dew point to many places, and the result is lethal for vertebrates like humans, fish, fowl, cattle, etc. Without mechanical cooling, of course. How do we do mechanical cooling after burning all of the fossil fuels? Add 8C to the ocean temperature, and West Antarctica melts. That is the best case. We lose most of the tropics. We also lose most low lying land, as most of the ice eventually melts.

Don’t let the uncertainty convince you that burning all the potential fossil fuels is a good idea. The science is settled.

To Phil Hays #6:
“Gravity has some significant uncertainties. Quantum gravity, around black holes, force unification, and more. Not very long ago, I could list gravity waves in this. We have just made a little progress…”

No.
For all PRACTICAL purposes, for man and beast on earth, gravity has no uncertainties.
(Now, the theory of *evolution* – to which some people often make a false equivalence with the *theory* of gravity – has some significant uncertainties, to put it mildly.)
…..
“If we burn all of the potentially available fossil fuels, we will increase the CO2 level in the atmosphere by about 4 times…If the climate sensitivity is low, we will only increase the surface temperature by about 8C…and the result is lethal for vertebrates like humans, fish, fowl, cattle, etc.”

No doubt some uncertainty on that 8C and on that lethality, yes?

But on the bright side, a couple things:

– All that extra CO2 will make the planet greener (i.e. more and healthier plants).

– Most people, including me, would appreciate warmer weather. And the people dying from cold are currently more than ten times the number dying from heat. We’ll be saving lives with a warmer planet!

– Living things, and particularly Man, are incredibly resilient and *adaptive* (just like good “evolving” things should be), even to significant climate changes.

– Some studies (uncertainly) say we’ll run out of natural gas and oil in about 50 years, coal in about 100.
So, after that relatively short span of time, global warming will end and we’ll start cooling off again. (Unfortunately, for some of us.)

To Phil Hays #6:
“Gravity has some significant uncertainties. Quantum gravity, around black holes, force unification, and more. Not very long ago, I could list gravity waves in this. We have just made a little progress…”

No.

Yes.
The point Phil Hays was making and which blasted over your head at Mach speeds is that the science is settled on the existence of gravity, even though we don’t know everything (hence “uncertainties”). In the same way, we know that global warming is occurring, is human caused and is certain to have very severe consequences unless dealt with (the science is settled) even though we don’t know everything (there are uncertainties).

I think the first thing those 13 experts will say about it is “yes, pretty picture, but what is the source of this data? It does not correspond to any reconstructions in the peer reviewed literature of the global temperature of the last ”

We could of course then go to some of that source data, like Wheeler’s cycles, but that’s been very much superceded, and did not go past the 1960s (so what is the data these people used after 1960?).

The 13 experts may also ask “Which archeologist claims the Vikings explored NE Canada around 1300? Last time we checked, it was around the year 1000!”

And when they find out that “Cliff Harris, climatologist” is not someone with any expertise in climate science…they’ll just get annoyed with people sending them on a wild-goose chase.

Yeah, I don’t know anyone who believes all of climate science is completely settled. And obviously there are still uncertainties in both measurements and expectations. That’s how it is for every field! Literally every single scientific data and model has uncertainties. Literally: every. single. one.

Obviously there are still things we need to study and we’d like to know better. (We’d like to nail the sensitivity down better, and regional changes, and precipitation, etc., etc.).

The point about global warming is that it’s settled enough to warrant taking action to reduce emissions. Just like the theory of gravity is settled enough for us to use it in engineering.

What does science say about the nearly irresistible urge to convince the unconvincable? I am prey to it myself, and must constantly remind myself of the futility of using logic to convince someone who has no chance whatever of accepting logic itself.

What does science say about the nearly irresistible urge to convince the unconvincable? I am prey to it myself, and must constantly remind myself of the futility of using logic to convince someone who has no chance whatever of accepting logic itself.

Well, SN isn’t here to be convinced, he’s here to prosecute his quixotic campaign against Godless science. For him to accept logic would be to admit defeat. OTOH there’s always the concern that some uncommitted lurker on the thread might need convincing, although the probability of that seems low.

Then there’s the fun to be had gleefully mocking resolute deniers like him. We’re entitled to have a little fun now and then, aren’t we?

– All that extra CO2 will make the planet greener (i.e. more and healthier plants).

– Most people, including me, would appreciate warmer weather. And the people dying from cold are currently more than ten times the number dying from heat. We’ll be saving lives with a warmer planet!

– Living things, and particularly Man, are incredibly resilient and *adaptive* (just like good “evolving” things should be), even to significant climate changes.

– Some studies (uncertainly) say we’ll run out of natural gas and oil in about 50 years, coal in about 100.

You do realize your points are all a load of crap, don’t you? These are just tired pseudoskeptic memes that have been answered many times over. The fact you persist in spreading manure — even when it’s been pointed out to you numerous times that most intelligent people don’t like being bombarded with shit — could be a reason you’re likely to be banned at any site that has a modicum of respect for veracity.

If you were interested in the truth there are plenty of people that would be willing to point you in the right direction, but they’d be wasting their time since your mind is already made up and not even a papal edict could change it.

Why only elicitation about CO2? It’s the main forcing affecting GW but seems also to be the best understood. I also thought most modeling shows a diminishing forcing RoR (i.e. if doubling is 3C, quadrupling is less than 6C). I would have liked to have seen questions regarding aerosols, water vapor, albedo, etc, and how sensitive they believe the climate response is to less understood drivers and feedbacks. Expert 4 gave the “surprise” answer in addition to a “normal” answer (not quite sure how that method works with statistics that should encompass “surprises” in the uncertainty,) I would have liked to have seen more questions to see how much agreement there is on which secondary effects are the largest component of error estimates and how much agreement there is on the individual components.

[The sensitivity to CO2 folds in all the other effects you’re asking about -W]